Chemistry based methods of manufacture for maxmet composite powders

ABSTRACT

A method of manufacturing a gas turbine engine air seal comprising forming at least one MAX phase particle. The method includes coating the at least one MAX phase particle with a metallic shell. The method includes applying the at least one MAX phase metallic coated particle to a surface of a substrate of the air seal to form an abradable layer of a MAXMET composite abradable material from the at least on MAX phase metallic coated particle.

CROSS-REFERENCE TO RELATED APPLICATIONS

The instant application is a divisional application of U.S. patentapplication Ser. No. 14/722,263, filed May 27, 2015, which claimsbenefit of U.S. Patent Application No. 62/003,159, filed May 27, 2014,and entitled “Chemistry Based Methods of Manufacture for MaxmetComposite Powders”, the disclosure of which is incorporated by referenceherein in its entirety as if set forth at length.

BACKGROUND

The disclosure relates to manufacture of materials used for enhancedabradable coatings for a gas turbine engine.

In compressor and turbine sections of a gas turbine engine, air sealsare used to seal the interface between a rotating structure, such as ahub or a blade, and a fixed structure, such as a housing or a stator.For example, typically, circumferentially arranged blade seal segmentsare fastened to a housing, for example, to provide the seal.

Relatively rotating components of a gas turbine engine are not at alltimes perfectly cylindrical or coaxial with one another during engineoperation. As a result, the relatively rotating components mayoccasionally rub against one another. To this end, an abradable materialtypically is adhered to the blade seal segments or full rings and/or therotating component.

Abradable seals in the compressor section of gas turbine engines includecharacteristics such as, good abradability, spall resistance, anderosion resistance. Abradable seals are required to exhibit a smoothsurface, low gas permeability, and environmental durability. The seal isa sacrificial element in order to minimize blade wear, so it isabradable. The seal must also minimize gas flow leakage through theseal, so a low gas permeability is desirable.

Abradable coatings for the seals are always a compromise betweenabradability and erosion resistance. In order to maintain blade tipclearances over time, the seal material needs to be tough and resistantto erosion. Conventional seal materials tend to be soft and weak inorder to have good abradability. Recently, MAXMETs (MAX phase reinforcedmetal matrix composites) have shown tremendous promise as nextgeneration compressor abradable coatings.

MAXMET composite coatings processed by powder metallurgy routes andthermal spraying techniques have showed excellent promise due toincreased erosion resistance, and significant reduction in coefficientof friction by incorporation of up to 50 vol. % MAX phases into currentabradable systems. The wear response of the newly developed coatingshave also showed significant changes in the rub mechanism. However, toscale up, methods of manufacture and processing parameters for enablingMAXMET applications as low and high temperature Low Pressure Compressorand High Pressure Compressor abradable coatings is currently underdevelopment. One of the challenges during use of thermal sprayingmethods to create abradable coatings is oxidation and low flow behaviorof MAX phase particles.

SUMMARY

In accordance with the present disclosure, there is provided a processto manufacture MAXMET particles by encapsulating the MAX phase particlesin a metallic shell, the choice of which depends on the end use of theabradable coating. The metal shell minimizes oxidation of the MAX phaseparticles during the spray process and permits a more efficient thermaldeposition of the MAXMET composite, which in turn contributes toimproved erosion resistance and abradability.

In accordance with the present disclosure, there is provided a method ofmanufacturing a gas turbine engine air seal comprising forming at leastone MAX phase particle. The method includes coating the at least one MAXphase particle with a metallic shell. The method includes applying theat least one MAX phase metallic coated particle to a surface of asubstrate of the air seal to form an abradable layer of a MAXMETcomposite abradable material from the at least one MAX phase metalliccoated particle.

In accordance with the present disclosure, there is provided chemicalmethods to clad MAX phase particles with a metallic shell to produceMAXMET particles for thermal spraying methods. Among these methods are,a) wet chemistry approach via a redox reaction to produce metallic shellfrom a metallic salt in a solution on the surface of MAX phaseparticles, b) combination of wet chemistry and gas reduction to makemetallic particles from metal oxides resulted from solution, c) chemicalvapor deposition, d) electrochemical reduction, and e) agglomeration offine (<5-10 micron) clad MAX phase particles during the plating processto form multi-particulate MAXMET domains of approximately 16-150 micronsize suitable for thermal spray deposition.

In accordance with the present disclosure, there is provided an air sealin a gas turbine engine comprising an abradable layer comprising aMAXMET composite material having MAX phase particles coated with ametallic shell.

In another and alternative embodiment the substrate is coupled to theabradable layer.

In another and alternative embodiment the metallic shell comprises Al orthe metallic shell comprises Ni.

In another and alternative embodiment the MAX phase is defined by theformula M_(n+1)AX_(n) where n is a number from 1 to 3.

In another and alternative embodiment a bond coat layer is adhered to atleast a portion of the substrate. The abradable layer is adhered to thebond coat.

In accordance with the present disclosure, there is provided a gasturbine engine comprising a first structure. A second structure isrotatable relative to the first structure, wherein one of the firststructure and second structure comprises a substrate. An abradable layeris coupled to the substrate wherein the abradable layer comprises aMAXMET composite material having MAX phase particles coated with ametallic shell.

In another and alternative embodiment the metallic shell comprises Ni orthe metallic shell comprises Al. The MAX phase is defined by the formulaM_(n+1)AX_(n) where n is a number from 1 to 3.

In accordance with the present disclosure, there is provided a method ofmanufacturing a gas turbine engine air seal comprises forming at leastone MAX phase particle. The method includes coating the at least one MAXphase particle with a metallic shell and applying the at least one MAXphase metallic coated particle to a surface of a substrate of the airseal to form an abradable layer of a MAXMET composite abradable materialfrom the at least one MAX phase metallic coated particle.

In another and alternative embodiment the coating step is selected fromthe group consisting of a redox reaction; a combination of wet chemistryand gas reduction; chemical vapor deposition, electrochemical reduction,and agglomeration of fine (<5-10 micron) clad MAX phase particles duringa plating process.

In another and alternative embodiment the method also includes theagglomeration of fine (<5-10 micron) clad MAX phase particles during theplating process to form multi-particulate MAXMET domains ofapproximately 16-150 micron size suitable for thermal spray deposition.

In another and alternative embodiment the step of applying the at leastone MAX phase metallic coated particle to a surface of a substrate ofsaid air seal comprises thermal spray deposition.

The details of one or more embodiments are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view of a portion of a gas turbine engineincorporating an air seal.

FIG. 2 shows a schematic view of an air seal.

FIG. 3 shows a cross sectional view of a coated MAX phase particlepowder before being applied.

FIG. 4 shows a MAXMET composite abradable coating on a substrate.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

FIG. 1 shows a portion of a gas turbine engine 10, for example, a highpressure compressor section. The engine 10 has blades 12 that areattached to a hub 14 that rotate about an axis 16. Stationary vanes 18extend from an outer case or housing 20, which may be constructed from anickel alloy, and are circumferentially interspersed between the turbineblades 15, which may be constructed from titanium in one example. Afirst gap 22 exists between the blades 12 and the outer case 20, and asecond gap 24 exists between the vanes 18 and the hub 14.

Air seals 26 (FIG. 2) are positioned in at least one of the first andsecond gaps 22, 24. Further, the air seals 26 may be positioned on: (a)the outer edge of the blades 12; (b) the inner edge of the vanes 18; (c)an outer surface of the hub 14 opposite the vanes 18; and/or (d) asshown in FIG. 2, on the inner surface of outer case 20 opposite theblades 12. It is desirable that the gaps 22, 24 be minimized andinteraction between the blades 12, vanes 18 and seals 26 occur tominimize air flow around blade tips or vane tips.

In one example shown in FIG. 2, the air seal 26 is integral with andsupported by a substrate, in the example, the outer case 20. That is,the air seal 26 is deposited directly onto the outer case 20 without anyintervening, separately supported seal structure, such as a typicalblade outer air seal. The tip of the blade 28 is arranged in close,proximity to the air seal 26. It should be recognized that the sealprovided herein may be used in any of a compressor, a fan or a turbinesection and that the seal may be provided on rotating or non-rotatingstructure.

The air seal 26 includes a bond coat 30 deposited onto the outer case 20or other structure/substrate. In an exemplary embodiment, the bond coat30 may be a thermally sprayed bond coat. In another example, the bondcoat 30 may comprise an alloy, such as a MCrAlY composition applied byair plasma spray. A composite topcoat 32 acts as an abradable layer thatis deposited on the bond coat 30 opposite the outer case 20. In anexemplary embodiment, the metallic bond coat 30 may be replaced by anadhesive layer. The adhesive may be polyurethane in the front stages ofthe compressor or in the fan where ambient temperature is sufficientlylow (e.g., less than about 300 degrees Fahrenheit.

The Referring also to FIGS. 3 and 4, in an exemplary embodiment, thecomposite abradable coating 32 comprises a MAX phase solids. In anexemplary embodiment the coating includes MAX phase particles 34. In anexemplary embodiment the MAX phase particles can include ternary carbideor nitride matrix material that may include MAX phases which are definedby the formula M_(n+1)AX_(n) where n is a number from 1 to 3. M is anearly transition metal element, A is an A group element, and X is carbon(C) or nitrogen (N). Early transition metals are any element in thed-block of the periodic table, which includes groups 3 to 12 on theperiodic table. A-group elements are mostly group IIA or IVA. The metalmatrix is at least one of a low, medium, and high melting point metal ormetal alloy. Low melting point metals or metal alloys are thoseapproximately in the range of from 100 degrees Centigrade to 300 degreesCentigrade. Medium melting point metals or metal alloys are thoseapproximately in the range of 300 degrees Centigrade to 1000 degreesCentigrade. High melting point metals or metal alloys are those in therange of 1000 degrees Centigrade and greater. MAXMET materials arecharacterized by excellent mechanical properties and improved toughness,high damage tolerance, high thermal stability and improved erosionresistance.

Examples of suitable MAX phase particles 34 include, but are not limitedto: ternary carbides and ternary nitrides. The atomic layers within theMAX phase particles 34 are layers of hard, strong, high modulus carbide.The atoms are also arranged in layers so that they form very weakcrystallographic planes. Thus, both high modulus strong planes and veryweak planes are present in matrix material 34. This results in kink bandforming tendencies, which gives it both ceramic and metallic properties.The kink bands provide toughness similar to a metal, making MAX phasematerial 34 capable of withstanding impact damage conditions while thehigh modulus and high hardness of the carbide layers make MAX phasematerial 34 capable of withstanding fine particle erosion. At the sametime, the slip planes have low strength such that MAX phase material 34is machinable using a sharp cutting point.

The MAX phase particles 34 can be encapsulated in a metallic shell 36 toform a MAXMET composite material 38. The metallic shell 36 can compriseany variety of materials depending on the end use of the abradablecomposite 32. In an exemplary embodiment, the metallic shell 36 cancomprise a Ni shell material for use with Ni-based abradable compositematerials. In another exemplary embodiment the metallic shell 36 cancomprise an Al shell for use with Al based abradable compositematerials. Besides Ni and Al, depending on the applications, othermetals, such as W, Co, Hf, Cr, and the like, can be applied as a coatinglayer.

The metallic shell 36 minimizes oxidation of the MAX phase particles 34during the spray application process. The metallic shell 36 permits moreefficient thermal deposition of the MAXMET composite material 38. Theefficient thermal deposition of the MAXMET composite material 38contributes to improved erosion resistance and abradability.

The metallic shell 36 cladding can be created by a variety of methods.For a given element, for instance, Al, certain procedures may be uniquein order to create good bonding to MAX phase. Among these methods are,a) wet chemistry approach via a redox reaction to produce metallic shellfrom a metallic salt in a solution on the surface of MAX phaseparticles, b) a combination of wet chemistry and gas reduction to makemetallic particles from metal oxides resulted from solution, c) chemicalvapor deposition, d) electrochemical reduction, e) agglomeration of fine(<5-10 micron) clad MAX phase particles during the plating process toform multi-particulate MAXMET domains of approximately 16-150 micronsize suitable for thermal spray deposition and f) electroless platingvia an auto-catalytic chemical reaction to produce nickel coatings onthe metal. The procedure and nickel bath (e.g. nickel chloride+hydratedsodium hypophosphite (NaPO₂H₂O) for electroless plating is commerciallyavailable and cost-effective. Methods c and d are ideal for fabricationof active metals with very negative electrode potentials, such as Al,Mg, and so on, which may not be able to be achieved with other methods.

The advantages of the methods described herein are easy handling, andscalability of metal synthesis/cladding. The metal shell 36 produced bythese processes can minimize oxidation of the MAX phase particles 34during the spray process and permits a more efficient thermal depositionof the MAXMET composite 38, which in turn contributes to improvederosion resistance and abradability.

One or more embodiments have been described. Nevertheless, it will beunderstood that various modifications may be made. For example, thepresent disclosure seeks to provide a method to manufacture MAXMETparticles by encapsulating the MAX phase particles in a metallic shell,the choice of which depends on the end use of the abradable, e.g. Nishell for Ni-based abradable coating materials or Al shell for Al-basedabradable coating materials. The metal shell minimizes oxidation of theMAX phase particles during the spray process and permits a moreefficient thermal deposition of the MAXMET composite, which in turncontributes to improved erosion resistance and abradability.Accordingly, other embodiments are within the scope of the followingclaims.

1. An air seal in a gas turbine engine comprising: an abradable layercomprising a MAXMET composite material having MAX phase particles coatedwith a metallic shell.
 2. The air seal of claim 1, further comprising: asubstrate coupled to said abradable layer.
 3. The air seal of claim 1,wherein said metallic shell comprises Al.
 4. The air seal of claim 1,wherein said MAX phase is defined by the formula M_(n+1)AX_(n) where nis a number from 1 to
 3. 5. The air seal of claim 1, wherein saidmetallic shell comprises Ni.
 6. The air seal of claim 1, furthercomprising: a bond coat layer adhered to at least a portion of thesubstrate; said abradable layer adhered to said bond coat.
 7. A gasturbine engine comprising: a first structure; a second structurerotatable relative to the first structure, wherein one of the firststructure and second structure comprises a substrate; and an abradablelayer coupled to said substrate wherein said abradable layer comprises aMAXMET composite material having MAX phase particles coated with ametallic shell.
 8. The gas turbine engine of claim 6, wherein themetallic shell comprises Ni.
 9. The gas turbine engine of claim 6,wherein the metallic shell comprises Al.
 10. The gas turbine engine ofclaim 6 wherein said MAX phase is defined by the formula M_(n+1)AX_(n)where n is a number from 1 to
 3. 11-15. (canceled)